^ETIOLOGY OF TUBERCULOSIS. 
77 
perish, only suppositions can be made, which cannot here be entered upon, but 
which I will discuss later. 
The further changes which complete themselves in tuberculous tissue after 
the formation of the epithelioid and giant cells are all of a regressive nature. 
For the greater part they belong in the sphere of the processes described by Wei- 
gert as necrosis of coagulation, and lead to the death or the tuberculously diseased 
tissue and to the formation of the so-called caseous masses which so frequently 
form the interior of the tuberculous herds. The tuberculous bacilli usually van¬ 
ish very quickly in the caseous masses, so that they are only to be met in young¬ 
er herds, and are almost always wanting in older ones. In other cases after the 
vanishing of the bacilli vegetation, the tuberculous tissue may simply shrink and 
be changed into firm cellular tissue. 
A very important property of the tuberculous bacilli must be mentioned 
here. It is the spore-forming property. As is well known, F. Cohn was the first 
to observe in the so-called hay-bacilli the appearance of shining little bodies which 
remained when the bacilli perished, had the power of germinating and growing 
to bacilli, and were to be considered the fruit form of the bacilli, receiving hence 
from F. Cohn the name of spores. 
The appearance of the spore formation as it shows itself microscopically in 
bacilli tinged with aniline colors, is to be seen in a very instructive manner on 
photograph No. 76, Plate 13, in the first volume of these communications. The 
bacilli appear there with short joints, and mostly consisting of two joints. Some 
of these joints are evenly dark colored and still resemble completely the spore- 
free bacilli on photograph 75. 
In many joints one notices, nevertheless, the appearance of a light point which 
increases in size gradually, while the colored contents of the joint withdraw 
more and more to the two ends, and the sides are bordered by fine lines marking 
the outlines of the joint. The bright space in the interior of the bacillus joint 
is the spore which in this specimen shows itself not by its brilliancy, since it is 
imbedded in a strongly light-refracting substance, but only by the absence of 
coloring material. With few exceptions the bacilli spores do not take the aniline 
coloring. The division into the articulation does not always appear so sharply 
defined as in the bacilli of this picture. 
In many sorts of bacilli, as for example in those belonging to inflamma- 
tion-of-the-spleen, the members appear closely joined together and form a con¬ 
tinuous thread which contains the uncolored spores at regular intervals. The 
spore formation of the tuberculous bacilli conducts itself in like fashion. The 
bacillus preserves its connection and does not fall apart into separate joints, but 
a bright body appears in every joint so that the bacillus after coloring resembles 
a little dark thread interrupted by bright egg-shaped spaces. By the use of the 
strongest systems and great magnifying power it may then be shown that the 
spore-bearing tuberculous bacillus presents exactly the same appearance as the 
spore-bearing bacilli of inflammalion-of-tlie-spleen, only in greatly diminished 
proportions. The spores are egg-shaped, bounded by a delicate colored line, and 
are present usually in the number of two to six in one bacillus. Since every sin¬ 
gle spore takes possession of one joint, from their numbers we can decide upon 
the number of the joints of the bacillus, that is to say of the single elements out 
